Led noise;

[Bernardduur]

Hey all!

I've just build a great looper box; 5 loops, 4 loops has clean blend functions and just a great sound......

The LEDs switching is special; I use a bypass knob to bypass all the loops. When you activate one loop in this bypass mode the LED colors red. When you hit the bypass knob (FX mode) the LED turns green. SO you can always see in what mode you are!!

Now I have a HUGE problem; the LEDs pop........ so I tried Jack Orman's LED pop noise fix but now the brightness of the LEDs go really down when I turn on multiple loops

It is orientated this way:
- All LED's are switched by ground
- I use dualcolor LED with three lugs; with the bypass switch I can switch between two paths the V+ can travel (red side of the LED / green side of the LED)
- the LED pop noise eliminator is orientated on the main V+ line before the switching
- All LED's are parallel

When I turn on one LED it is normal bright, but when I turn on more LEDs the brightness go down quick The pops are gone

Any ideas?

[Mark Hammer]

The pop is partly because of current draw.  Are you using "ultrabright" LEDs?  If not, try them and see if it makes a difference.  I don't know if there is an official value, but I would consider anything with a brightness rating of over 2000mcd (millicandles) to be ultrabright.  These can be run at a fraction of the current of "regular" LEDs (500mcd and less) and still be easily seen.  As well, you can reduce current draw even more if you try to increase visibility by mounting them against a dark surround (e.g., black bezel).  Obviously the current draw does not reduce itself.  Rather, you can use a much higher value of current-limiting resistor with them and still get a decent brightness.

[Bernardduur]

It is the same with ultrabright LED's

The background is already black and I can see them but they are so weak........ even when I split the path in two the brightness decreases big time...... With only one on it is just normal.

I thought when LED's are in parrallel they share the same voltage THUS all should be of equal brightness...... If I omit the pop-reducing circuit (and introduce popping) they do some of the same thing (not as weak but weaker then bright). If I then add a resistor to each ground connection they all burn equally bright.

Here is the page

I'll try to reduce R2

[Pushtone]

2000mcd (millicandles) to be ultrabright. 

I was wondering what that "mcd" meant. Thanks!
I was able to find this now "1000 millicandela equals 1 candela". Ah, metric, just makes sense don't it.


The super bight with low forward current is the path I went when I had poping issues. As suggested on the forum.

I was using 300-500mcd LEDs and 1k resistors (not that bright and washed out by stage lighting).

I replaced all the LEDs in my pedals with 2500mcd (red) leds and 10k resistors.
This fixed the poping problem with several plagued pedals.

But now the LED is SO bright it creates an corona in my eye that blocks me from seeing the knobs clearly.
In a dimly lit room I can see the LED reflecting off the 8 ft. ceiling. Fixed one problem and created another.

[Mark Hammer]

You can easily increase the value of that 10k current limiting resistor to 15k or more.  I have an 18k in series in one of my pedals.  It's not other-side-of-the-stage bright, mind you, but visible, even against a white background in broad daylight.

It may be more trouble than it's worth, but one might consider use of a suitable trimpot (25k ought to be fine for all purposes and brightnesses).

[Bernardduur]

Shame there are no ultrabright dual LED's around here

I "fixed" it by replacing the 4.7k resistor with a 100 ohms version which made the LED's clearly visible again and when all are on they still light up strong enough

[Meanderthal]

 Is 100 ohms enough to protect them from being burnt? I went down as far as 680 Ohms, but have been nervous about attempting lower than that... Yeah, I know, specs (but I seldom have them anyway), and they're cheap enough that a few lost to learn is no biggie... just thought I'd ask...

And, I have noticed that the others dim in multi-effects boxes, but just figured it was current draw. I can still see 'em fine...

[Bernardduur]

Well, there is still a 390 ohm resistor in series with it so I guess it will work........

But the 100 ohm does now add popping to the signal...... so I am back where I started. I will search for some brighter ones!

[R O Tiree]

Sounds to me as though you are just using the one anti-pop circuit, yes? This explains why they get dimmer as you engage more. The diodes are in parallel, have broadly similar Vf and therefore you are dividing the available current between them.

In order to stop the dimming, you will have to put an anti-pop circuit ahead of each one - ie one circuit for each red/green pair.

As far as the popping goes, some (cheaper?) switches have a certain amount of cross-talk between the segments of the switch. No amount of anti-pop circuitry will stop it, if that is the case. That might be worth investigating.